Interferometric fiber-optic gyroscopes are being increasingly used in medium to high performance inertial applications. For example, interferometric fiber-optic gyroscopes are used in inertial navigation applications, such as in military applications of a tactical nature (i.e., of short range, short time, and lower performance) and of a strategic nature (i.e., of long range, long time, and higher performance). Interferometric fiber-optic gyroscopes are also used in many commercial applications. As one example, a tactical-grade interferometric fiber-optic gyroscope is used to stabilize the yellow line projected on the ground during a televised football game to indicate the point that must be crossed by the offense to make a “first down.”
An interferometric fiber-optic gyroscope typically uses an integrated-optic bias phase modulator to introduce a non-reciprocal phase shift to counter-propagating light beams to aid in the measurement of the inertial rate of the gyroscope. The bias phase modulator is typically biased by a signal that oscillates at the eigenfrequency of the gyroscope, which is equal to the inverse of twice the transit time of the gyroscope's fiber coil. A rotation rate detector signal, which contains information regarding the inertial rate of the gyroscope, may also oscillate at the eigenfrequency. Typically, both signals are transmitted via different but proximate wires, and thus the rotation rate detector signal is susceptible to interference from the bias phase modulator signal. Because the bias phase modulator signal must be large to obtain high gyroscope sensitivity and because the detected rotation rate signal is very small for small inertial rates, isolation requirements between the bias phase modulator signal and the rotation rate detector signal are very high, for example as high as 160 dB for high-performance gyroscopes. It is nearly impossible, however, to obtain this required isolation in practice. Because the bias phase modulator signal is often routed throughout the system and may even share the same connector(s) as the sensitive rotation rate detector signal, there are many potential opportunities for corruption of the rotation rate detector signal by the bias phase modulator signal.